Process for the fibrous esterification of cellulose



Patented Nov. 5, 1935 UNITED STTES PROCESS FOR THE FIBROUS ESTERIFI- CATION OF CELLULOSE Carl J. Malm and Charles L. Fletcher, Rochester, N. Y., assigncrs to Eastman Kodak Company, Rochester, N. Y., a corporation of New York No Drawing. Application October 1, 1932, Serial No. 635,856

17 Claims.- (01. 260-101) The present invention relates to the fibrous esterification of cellulose in Which an ether having a boiling point higher than C. is employed as the non-solvent or diluent in the esterification bath proper.

The processes for the esterification of cellulose at the present time may be broadly divided into the two classes of (1) the dope-forming and (2) the fibrous or non-dope-forming types. We have disclosed and claimed a process of the latter type in our application Serial No. 590,509 filed February 2, 1932 in which an ether having a boiling point higher than 70 C. is employed as a nonsolvent or diluent in the esterification of cellulose, in the customary manner. This customary manner comprises the addition of the non-solvent to the pretreatment mixture.

We have now found that in the esterification of cellulose by a fibrous method employing a higher ether, when the ether is added not to the pretreatment but to the esterification step proper the time for the completion of the reaction is greatly reduced. We have also found that in a process according to our invention a productis formed which gives a more brillian dope in the common solvents than an ester prepared by the fibrous esterification of cellulose according to previous methods. We have found that in the case of our invention there is present in the ester mass formed only a minimum of unesterified products such as fiber or grain.

Our process broadly comprises the esterification of cellulose by pretreating the cellulose with the usual pretreatment bath such as a fatty acid or acids with or without a catlyst, then'treating the mass with an esterification bath comprising mainly one or more fatty acid anhydrides in the presence of a catalyst. The ether may be added to the esterification bath according to our invention either at the same time as the other esterification ingredients or at any time thereafter up to the time when the desired softeni'ngaction by the esterification ingredients has been obtained or in other Words up to that point at which the cellulose ester may go into solution unless this or some other non-solvent be added.

The ideal condition for carrying out curinvention which in practice should be approached as nearly as possible by those performing the process, is to add the non-solvent to the esterification mixture at such a rate and in such a total amount as to keep the reaction mixture just an increment below the solubility point.

Example I 50 lbs. of cellulose was pretreated for about 3 hours at approximately 150 F. with a mixture of 175 lbs. of 100% propionic acid and 50 lbs. 5 of glacial acetic acid. The mass was then cooled to a temperature of about 70 F. and a mixture of 100 lbs. of acetic anhydride, 75 lbs. of propionic anhydride and .2 1b. of 70% perchloric acid was added thereto. The 10 whole was maintained at a temperature of 75 F. fon 1 hour at the end of which time 150 lbs. of iso-amyl ether Was added thereto. The temperature of the mass was then uniformly increased from 75 to F. over a period of 4 15 hours and was held at that temperature for about 4 or 5 hours or until solubility in acetone was obtained. The product, cellulose acetatepropionate, was washed free of acid with isoamyl ether and was freed of the residual ether 20 by applying heat thereto.

Example II 50 lbs. of cellulose was pretreated for 3 hours at about 100 F. with a mixture of 250 lbs. of 25 glacial acetic acid and 3 lbs. of a catalyst consisting of 1 part of sulfuric acid and 2 parts of phosphoric acid. The mass was then cooled to approximately 70 F. and. lbs. of 85% acetic anhydride was then added. After maintaining 'driven off as in the preceding example. The product was stabilized by treating it with boiling n-amyl alcohol for several'hours such stabilization process being disclosed and claimed in application Serial No. 635,854 of C. J. Malm and C. R. Fordyce filed of even date herewith.

Example III 50 lbs. of cellulose was pretreated for 3 hours at 150 F, with 150 lbs. of 100% butyric acid and 50 lbs. of glacial acetic acid. The mass was then 50 cooled to a temperature of 70 F. and a mixture of 100 lbs. of 85% acetic anhydride 100 lbs. of 100% butyric anhydride, 25 'lbs. of n-butyl ether,

1 lb. of sulfuric acid and 2.7 lbs. of phosphoric acid was added. The temperature of 70 Fpwas 55 maintained for one hour after which 125 lbs. of n-butyl ether was added and the temperature was uniformly increased to 120 F. over a period of 10 hours. The temperature was maintained at 120 F. for about 20-25 hours or until the fibers in the bath were found to be soluble in acetone. The fibers were then separated from the bath, washed free of acid with n-butyl ether and dried by applying heat. The product, cellulose acetatebutyrate may be stabilized by treating with an alcohol at an elevated temperature as set forth in the preceding example.

Example IV The procedure of the preceding example was duplicated except that instead of the n-butyl ether being added in two parts it was added continuously after the addition of the anhydrides and at such a rate as to keep the fibers just insoluble in the esterification bath. This condition of just insoluble in the esterification bath may be determined by the appearance of the fibers which condition is easily recognized by those skilled in the art.

As pointed out above, the ethers having a boiling point about 70 C'., especially the aliphatic ethers, may be employed as the non-solvent in the esterification of cellulose. In addition to the normal ethers which the examples show are suitable, isomeric ethers such as iso-amyl ether, iso-butyl ether etc. may be employed.

An important feature of the use of a higher boiling ether as a diluent in an esterification process is that that process may be carried out in the presence of only a relatively small amount of catalyst. Processes in which an appreciable amount of catalyst, such as sulfuric acid, is employed often result in a product of little, if any, value. The large amount of catalyst in such processes apparently has a marked degrading action on the cellulose which may even result in the conversion of the cellulose to a cellobiose or some other compound resulting from the degradation of cellulose.

Cotton linters is preferred as the starting material in the examples as due to its economy and satisfactory susceptibility to esterification that material is usually employed in the preparation of cellulose esters at the present time. Other cellulosic materials such as cotton fibre tissue paper, clean cotton, surgical cotton wool (preferably bleached) and carefully prepared sulfite wood pulp which has been bleached may however be employed as the starting material if desired. Also easily esterifiable cellulosic materials such as so-called hydro-cellulose, reverted cellulose such as may be derived from the viscose or cuprammonium process and even cellulose nitrates, acetates, formates or ethers, which contain free hydroxyl groups available for esterification by processes carried out according to our invention, are also suitable as the starting material of our process of preparing cellulose esters. The term cellulosic material as employed herein refers to materials comprising either cellulose none of Whose hydroxyl groups have been replaced or cellulose which has been partially esterified or etherified but which still contains free and esterifiable hydroxyl groups.

Various conditions in the carrying out of the esterification of cellulose according to our invention may be varied in accordance with the judgment of the individual operator. modifications such as the employment of other Various other anhydrides and acids are apparent to those skilled in the art. For example a substituted fatty acid anhydride such as a chloracetic anhydride as disclosed in Clarke and Malm application Serial No. 179,177 filed March 28, 1927, now 5 Patent No. 1,880,808, Oct. 4, 1932, may be employed instead of or supplementary to the unsubstituted anhydrides and/or substituted fatty acids such as chloracetic or alkoxyacetic acid may be employed instead of or supplementary to the unsubstituted acids the only condition being that a source of acyl groups is provided in the reaction mixture.

We claim:

1. In the fibrous esterification of cellulose in which the cellulose is pretreated with a lower fatty acid and then esterified, the step which comprises incorporating an unsubstituted aliphatic ether having a boiling point above 70 C. in the esterification mass at a point subsequent to the mixing of the esterifying materials with the cellulose but before the dissolution of the resulting ester in the esterification bath would otherwise occur.

2. In the fibrous esterification of cellulose in which the cellulose is pretreated with a lower fatty acid and then esterified, the step which comprises incorporating an unsubstituted aliphatic ether having a boiling point above 70 C. in the esterification mass shortly after the pretreated cellulose has been mixed with the esterifying bath.

3. In the fibrous preparation of a cellulose acetate-propionate in which cellulose is pretreated with a lower fatty acid and then esterified, the step which comprises incorporating an unsubstituted aliphatic ether having a boiling point above 70 C. in the esterification mass in a step subsequent to the mixing of the esterifying materials with the cellulose but before its dissolution would otherwise occur.

4. In the fibrous preparation of a cellulose acetate-propionate in which cellulose is pretreated with a lower fatty acid and then esterified, the step which comprises incorporating an unsubstituted aliphatic ether having a boiling point above 70 C. in the esterification mass shortly after the pretreated cellulose has been mixed with the esterifying bath.

5. In the fibrous acetylation of cellulose in in the esterification mass in a step subsequent to the mixing of the esterifying materials with the cellulose but before its dissolution would otherwise occur.

6. In the fibrous acetylation of cellulose in which the cellulose is pretreated with a lower 0 fatty acid and then esterified, the step which comprises incorporating an unsubstituted aliphatic ether having a boiling point above C. in the esterification mass shortly after the pretreated cellulose has been mixed with the esteri- 5 fyihg bath.

7. In the fibrous esterification of cellulose in which the cellulose is pretreated with a lower fatty acid and then esterified, the step which comprises incorporating an amyl ether in the 70 esterification mass subsequent to its pretreatment but before its dissolution would otherwise occur.

8. In the fibrous esterification of cellulose in which the cellulose is pretreated with a lower fatty acid and then esterified, the step which comprises incorporating an iso-amyl ether in the esterification mass subsequent to the mixing of the esterifying materials with the cellulose but before its dissolution would otherwise occur.

9. In the fibrous preparation of a cellulose acetate-propionate in which cellulose is pretreated with a lower fatty acid and then esterified, the step which comprises incorporating an amyl ether in the esterification mass subsequent to the mixing of the esterifying materials with the cellulose but before its dissolution would otherwise occur.

10. In the fibrous preparation of a cellulose acetate-propionate in which cellulose is pretreated with a lower fatty acid and then esterified, the step which comprises incorporating isoamyl ether in the esterification mass subsequent to the mixing of the esterifying materials with the cellulose but before its dissolution would otherwise occur.

11. In the fibrous esterificationof cellulose in which the cellulose is pretreated with a lower fatty acid and then esterified, the step which comprises incorporating an unsubstituted aliphatic ether having a boiling point about 70 C. in the esterification mass subsequent to its pretreatment but within not more than approximately one hour after the cellulose has been immersed in the esterifying bath.

12. In the fibrous esterification of cellulose in which the cellulose is pretreated with a lower fatty acid and then esterified, the step which comprises incorporating an ether selected from the group consisting of iso-amyl ether, n-propyl 1 ether and n-butyl ether in the esterification mass subsequent to the miin'ng of the esterifying materials with the cellulose but before its dissolution would otherwise occur. 7

13; In the fibrous esterification of cellulose in which the cellulose is pretreated with a lower fatty acid and then esterified, the step which comprises incorporating an amyl ether in the esterification mass subsequent to its pretreatment but within not more than approximately one hour after the cellulose has been immersed in the esterifying bath.

14. In the fibrous esterification of cellulose in which the cellulose is pretreated with a lower fatty acid and then esterified, the step subsequent to the pretreatment which comprises continuously adding to the esterification bath after the addition of cellulose, an unsubstituted aliphatic ether having a boiling point above 70 C. at a rate which will maintain the bath nonsolvent of the cellulose material while it is undergoing esterification.

15. In the fibrous esterification of cellulose in which the cellulose is pretreated with a lower fatty acid and then esterified, the step subsequent to the pretreatment which comprises continuously adding to the esterification bath, after the addition of the pretreated cellulose thereto, an ether selected from the group consisting of iso-amyl ether, n-butyl ether and n-propyl ether at a rate which will maintain the bath nonsolvent of the cellulose material while it is undergoing esterification.

16. In the fibrous esterification of cellulose in which the cellulose is pretreated with a lower fatty acid and then esterified, the step subsequent to the pretreatment which comprises continuously adding to the esterification bath, after the addition of thepretreated cellulose thereto, an amyl ether at a rate which will maintain the bath non-solvent of the cellulose material while it is undergoing esterification.

17. In the fibrous preparation of a cellulose acetate-propionate in which the cellulose is pretreated with a lower fatty acid and then esterified, the step subsequent to the pretreatment which comprises continuously adding to the esterification bath, after the addition of the pretreated cellulose thereto, an unsubstituted aliphatic ether having a boiling point about 70 C. at a rate which will maintain the bath nonsolvent of the cellulosematerial while it is undergoing esterification.

CARL J. MALM. CHARLES L. FLETCHER. 

